P0871: Transmission fluid pressure sensor or switch C reading out of range

Transmission fluid pressure sensor/switch C circuit range/performance

Severity: Inspect soon

Kelley Blue Book rates P0871 very serious and says to avoid driving with it, so it should be inspected promptly.

It gets more serious if:

Stop: Stop driving and have the car towed if the transmission slips, overheats, smells burnt or smokes. Kelley Blue Book says to avoid driving with P0871.

P0871 in short

P0871 means the signal from transmission fluid pressure sensor or switch C does not match what the computer expects. A failed sensor, circuit fault, low fluid or an internal problem can cause it. Subaru fixes some 2022 Outbacks with a computer reprogram. Kelley Blue Book says avoid driving it; have it checked promptly.

The computer compares the fluid pressure sensor or switch C reading with what it commanded. If the two do not agree, it sets P0871. Which circuit C is depends on the transmission.

Kelley Blue Book lists a failed sensor, a faulty circuit, low fluid, internal problems and leaks. Symptoms include overheating, slipping, a burning smell and smoke.

Manufacturers have bulletins: Subaru offers a TCM reprogramming file for P0871 on the 2022 Outback; GM tells dealers to clear and retest P0871 on the 2015 Spark and replace the transmission or valve body if it returns; Ram lists P0871 with P0765 and P0755 on a 2022 Ram 2500.

Most likely causes

Cause 1: Failed sensor or faulty sensor circuit
Common general cause
Why it ranks here
Kelley Blue Book lists a failed sensor and a faulty circuit first, and has the sensor, connections and reference voltage tested.
What would change this
Rises if reference voltage or ground is out of range. Falls if the circuit tests good.
Cause 2: Low fluid or a leak
Common general cause
Why it ranks here
Kelley Blue Book lists low fluid and leaks and has fluid level and condition checked first.
What would change this
Rises if fluid is low or leaking. Falls if normal.
Cause 3: TCM software (2022 Subaru Outback)
Supported by vehicle data
Why it ranks here
Subaru 16-135-21R is a TCM reprogramming file for P0871, with a companion bulletin on diagnosis for the Outback Wilderness.
What would change this
Rises on a covered Outback. Falls on other vehicles.
Cause 4: Internal transmission or valve body problem
Supported by vehicle data
Why it ranks here
Kelley Blue Book lists internal problems, and GM PIP5521 has dealers replace the transmission or valve body on the 2015 Spark if P0871 returns after clearing.
What would change this
Rises if the code returns after a clear and the circuit tests good. Falls if clearing and retest resolves it.

What to test first

Start at step 1. Each result tells you what it means and where to go next.

Step 1: Read all stored codes, noting any solenoid codes stored with P0871 (Ram lists P0765 and P0755 with it).
Low riskTool: OBD-II scan tool
- IfP0871 alone on a 2022 Subaru Outback
  It meansAsk about the TCM reprogramming bulletin.
  Go to step 2
- IfOther codes are stored
  It meansDiagnose those with P0871.
  Go to step 2
Step 2: Ask a dealer whether your VIN has a bulletin or software update for P0871.
Low risk
- IfA TCM reprogram applies
  It meansDo it before replacing parts.
  Points to: TCM software (2022 Subaru Outback)
- IfNo update applies
  It meansCheck fluid.
  Go to step 3
Step 3: Check the transmission fluid level and condition by the method in the owner's manual. Many transmissions have no dipstick; leave those to a shop.
Use cautionTool: transmission dipstick, if fitted
Warning:Run the check only as the owner's manual describes; the transmission is hot and has moving parts nearby.
- IfFluid is low, burnt or leaking
  It meansFix the leak and service the fluid.
  Points to: Low fluid or a leak
- IfFluid is normal
  It meansHave the sensor circuit tested.
  Go to step 4
Step 4: Have a shop test the sensor, its connector, reference voltage and ground, and the transmission pressure.
Best left to a shopTool: scan tool, multimeter, pressure gauge
Warning:Transmission work involves hot fluid and heavy, moving parts; leave this to a shop.
- IfReference voltage or ground is out of range
  It meansRepair the circuit.
  Points to: Failed sensor or faulty sensor circuit
- IfCircuit is good and pressure is wrong
  It meansInternal or valve body problem is likely.
  Points to: Internal transmission or valve body problem

Symptoms

Check engine light
Transmission slipping or fails to engage a gear Gets more serious: stop and have it checked.
Transmission overheating, burning smell or smoke Gets more serious: stop and have it checked.

How to fix

Step 1: Ask a dealer whether your VIN has an open bulletin or software update for P0871.

On your vehicle

Subaru

2022 · Outback
Supported by vehicle data
Subaru 16-135-21R provides a TCM reprogramming file for P0871 on the 2022 Outback; 16-134-21 adds diagnostic information for the Wilderness. Whether they are still current is not verified.

16-135-21RStatus unverified
TCM reprogramming for P0871
2022outback · NHTSA 10203874
Reprogramming file for the TCM to address P0871. Only the NHTSA summary was read.
We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.
16-134-21Status unverified
Additional diagnostic information for P0871 (Wilderness)
2022outback · NHTSA 10202836
Additional diagnostic information; the summary says nothing more.
We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

Chevrolet

2015 · Spark
Supported by vehicle data
GM PIP5521 tells dealers to clear and retest P0871 on the 2015 Spark and replace the transmission or valve body if it returns. Whether it is still current is not verified.

PIP5521Status unverified
Spark P0871 or P2714 in the TCM
2015spark · NHTSA 10157006
Clear codes and retest; if they return, replace the transmission or valve body depending on model year. Only the NHTSA summary was read.
We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

All Transmission codes

Sources and review

P0871 OBD-II Trouble Code: Transmission Fluid Pressure Sensor/Switch C Circuit Range/Performance — Kelley Blue Book
Subaru 16-135-21R: TCM reprogramming for P0871 — Subaru / NHTSA
Subaru 16-134-21: Additional diagnostic information for P0871 (Outback Wilderness) — Subaru / NHTSA
GM PIP5521: Spark P0871 or P2714 in the TCM — General Motors / NHTSA
Ram SOL S2121000008 Rev C: MIL with P0765, P0871 and/or P0755 — Ram (Stellantis) / NHTSA

Last reviewed: October 15, 2026
Written by: Saurabh K.
Editorial review: Pending
Technician review: Technician review pending

This page explains what a code usually means; it is not a substitute for a professional inspection. How we source and review · Report an error

Severity: Inspect soon

Most likely causes

Cause 1: Failed sensor or faulty sensor circuit

Cause 2: Low fluid or a leak

Cause 3: TCM software (2022 Subaru Outback)

Cause 4: Internal transmission or valve body problem

What to test first

Step 1: Read all stored codes, noting any solenoid codes stored with P0871 (Ram lists P0765 and P0755 with it).

Step 2: Ask a dealer whether your VIN has a bulletin or software update for P0871.

Step 3: Check the transmission fluid level and condition by the method in the owner's manual. Many transmissions have no dipstick; leave those to a shop.

Step 4: Have a shop test the sensor, its connector, reference voltage and ground, and the transmission pressure.

Symptoms

How to fix

On your vehicle

SubaruYour car

ChevroletYour car

Related codes

Sources and review

Subaru

Chevrolet